Transformer protective switch



June 24, 1930 w DlCKlNSON 1,768,398

TRANSFORMER PROTECTIVE SWITCH Filed July 2, 1928 In Vc-zntor-I Willam- K. DiOKihSQn, Joy His Attorney Patented June 24, 1930 UNITED STATES PATENT OFFICE WILBUB, K. DICKINSON, OF LYNN, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK TRANSFORMER PROTECTIVE SWITCH Application filed July 2, 1928.

The present invention relates to transformers and while it is not limited thereto necessarily, it finds especial utility in connection with current transformers. For this reason the invention is here illustrated and described as applied to a current trans former.

The object of the invention is to provide in connection with a transformer such as a current transformer, an improved protective device for protecting the windin s of the transformer from overloads, and or a consideration of what I believe to be novel and my invention, attention is directed to the ac- 16 companying description and the claims appended thereto. a

Referring to the drawing, Fig. 1 is a perspective view of a current transformer provided with a protective device embodying my invention, and Fig. 2 is a diagrammatic view illustrating the circuit arrangement.

Referring to the drawing, 5 indicates a current transformer of suitable construction provided with a primary winding 6 and a 2 secondary winding 7. 8 and 9. indicate the two terminals of the primary winding. In Fig. 2, 10 indicates a measuring instrument connected to the secondary winding of the transformer.. The arrangement illustrated )0 is to be taken as typical of any suitable transformer construction.

According to my invention I provide a conductor 11 associated with the primary winding 6 of the transformer and adapted to be connected in shunt with the primary winding in case of overload on the transformer, the arrangement being such that conductor 11 is automatically connected in shunt to the primary winding upon the occurrence of an overload and is, in the present instance, automatically disconnected as soon as the overload subsides. According to the embodiment of the invention illustrated in the drawing, I connect one end of conductor 11 to primary winding terminal 8 and I connect the other end to a contact 12, which forms the stationarycontact of a circuit closer. In the present instance, contact 12 forms a continuation of and is a part of Serial No. 289,730.

conductor 11 which with advantage may be in the form of a flat bar.

The movable contact of the circuit closer comprises a flat bar 13 carried by and forming a part of the armature 14 of an electromagnet. Contact 13 and armature 14 are carried by a frame 15 provided with guides 16 which slide on vertical posts 17 mounted on a base plate 18 which in turn is carried by a suitable support 19 formed of insulating material. The upper ends of posts 17 are connected by across bar 20. 21 indicates vertically-adjustable stops on posts 17 which serve to limit upward movement of frame 15. Frame 15 is normally biased into engagement with stops 21 by a spring 22 connected to cross piece 20. Contact 13 is connected by bolts 23 to arms 24 which form a part of frame 15, the bolts passing loosely through holes in the arms and being provided with wing nuts on their outer ends. Surrounding bolts 23 between arms 24 and conductor clamps 25 are springs 23 which serve to yieldingly hold contact 13 in the position shown in Fig. 1 of the drawing. The compression of springs 23 may be adjusted by means of the wing nuts. The arrangement serves to permit contact 13 to move a ainst the action of springs 23 when it is orced into engagement with stationary contact 12. Mounted on base 18 is a laminated structure 26 which forms the core of the electromagnet. The face of the laminated structure is provided with a transversely extending groove in which is located a straight, flat bar 27 which forms the winding of the electromagnet. At its one end, bar 27 is connected to terminal 9 of the primary winding and at its other end is connected to the circuit conductor 28. Contact 12 is carried by a body of insulation 29 which rests on bar 27. Movable contact 13 is electrically connected to bar 27 by suitable connectors 30. In the resent instance, connectors 30 are shown as ing in the form of flexible circular bands clamped to contact 13 by the clamps 25 and clamped. to bar 27 by suitable clamps 31. In

1, the left hand connector 30 is broken away order to show certain parts more clearly.

The protective device isconnected in series with the transformer as is illustrated in the drawing. Normally spring 22 holds contact 13 in its uppermost position and out of engagement with contact 12. The spring is adjusted so that for normal loads on the thereby protecting the transformer from the overload. However, there remains a sufiicient amount of current passing through the primary of the transformer so that the secondary will deliver enough current, to operate such relays or other protective devices as may be connected with it.

I have found that a protective device of this type when properly designed after the manner dlsclosed in the drawing can be made to operate in' a small fraction of a second and'with ample speed to readily protect the transformer. For example the protective device may he made to operate with a speed of the order of one-thousandth (1/1000) of a second.

As soon as the current decreases again below the predetermined high value, spring- 22 serves automatically to lift contact 13 from engagement with contact 12 thus opening the shunt circuit. WVith this arrangement, it will be seen that the operation of the protective device is entirely automatic in both directions. This is an important feature of the invention since it means that the protective device requires no attention on the part of an operative and no manual resetting.

When desirable, I may provide in connection with the electromagnetic circuit closer, a second circuit closer which is closed when ever the electromagnetic circuit closer is closed and which functions to open a suitable circuit breaker such as an oil circuit breaker in the main circuit of the transformer primary. This arrangement may be used in combination with an overload relay in the secondary circuit of the transformer.

32 indicates a contact carried by the movable frame 15 and adapted, when the frame moves downward, tobridge a pair of contacts 33. Contacts 33 are connected to the trip coil 34 of a circuit breaker 35 located in the main lead of the primary transformer winding 6. With this arran ement it will be seen that whenever the electromagnetic circuit closer moves downward to bring contact 13 into engagement with contact 12, contact 32 bridges contacts 33, thereby effecting the opening of the circuit'breaker 35.

In the circuit of the secondary transformer winding is an overload relay 36 which, when actuated, closes a circuit on trip coil 34 to effect opening of circuit breaker 35. Over' load relay36 may be set to operate at a load somewhat lower than that at which the electromagnetically-operated protective circuit closer operates. Ordinarily it will be a slower acting piece of mechanism than the electromagnetically-operated circuit closer. In the case of a short circuit, for example, the electromagn'etically-operated circuit closer would function to connect conductor 11 in shunt to the primary transformer winding and open switch 35 before the overload relay 36 would operate.

As stated above, my invention possesses especial utility in connection with current transformers. Heretofore it has been the practice and has been found necessary to make current transformers of a sufficiently large size ,to withstand the overloads met with. As a result, they have been much largerthan have been necessary for normal operation. This has added materially to their size and cost. By my invention I am enabled to reduce very materially the size of current transformers for a particular application, being able to reduce them in size by an amount of the order of two-thirds.

'As a result the current transformer with its protective device are together not as large as the current transformer alone prior to the application of my invention. The result is a saving in cost and size of the instruments.

In accordance with the provisions of the patent statutes I have described the principle of operation of my invention, together with the apparatus which I now consider to rep resent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative andthat the invention may be carried out by other means.

IVhat I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electro-magnetically operated circuit closer for use as-a protective device comprising a stationary magnetic core structure having a transverse slot, a bar which extends through said slot and forms the winding of an electromagnet, a contact carried by and insulated from said bar, a movable contact structure which forms the armature of the electromagnet, and flexible conductors connecting the movable contactstructure to said bar.

2. Anelectro-magnetically operated circuit closer for use as a protective device comprising a stationary magnetic core structure, a movable magnetic core structure, and a 1,7ea,aes

current carrying conductor two contacts extendlng between said core structures, one of said contacts being connectedto said movable core structure to be moved thereby toward and from said other contact, and a conductive connection between said movable contact and said conductor.

3. An electro-magnetically operated circuit closer for use as a protective device comprising a stationary magnetic core structure, a movable magnetic core structure, and a current carrying conductor -and two contacts extending between said core structures said conductor and one of said contacts being stationary, the other of said contacts being movable, said stationary contact extending between said conductor and said movable contact, said movablev contact being connected to said movable core structure to be.

moved thereby toward and' from said stationary contact, and a conductive connection between said movable contact and said conductor.

In witness whereof, I have hereunto set my hand this 27th da of June 1928.. k WlLB K. DIKINSON. 

